The present invention relates to a power supply apparatus that drives a motor for running an electric vehicle, such as a hybrid car or an electric car, and particularly to a power supply apparatus for a vehicle capable of accurately detecting a leakage that occurs on the output side of a driving battery with simple circuit configuration.
High voltage is required to increase the output of a power supply apparatus for driving an electric vehicle. The reason is that the output is proportional to the product of a voltage and a current, and that a higher voltage provides an advantage when a motor is driven. For example, the output voltage of a power supply apparatus for driving a hybrid car or an electric car is a very high voltage of 200 V or more. Since workers may receive an electric shock if they touch a high voltage power supply apparatus during maintenance, the high voltage power supply apparatus is not connected to a chassis for reasons of safety. For this reason, this type of power supply apparatus has the ability to measure a leakage resistance in order to disconnect a circuit when an electric shock is detected. The leakage resistance is a resistance between the power supply apparatus and the chassis. FIG. 1 shows a circuit for measuring the leakage resistance in a power supply apparatus. A leakage detection circuit 50 shown in this Figure has a leakage detection resistance 51, a leakage detection switch 52, and a voltage detection circuit 53 that detects the voltage produced across the leakage detection resistance 51. When a leakage resistance Rr exists, in the state where the leakage detection switch 52 is ON, a current flows through the leakage detection resistance 51. Accordingly, a voltage across the leakage detection resistance 51 is measured, and, leakage can be detected.
As shown in this Figure, a power supply apparatus that detects a voltage in a particular portion to detect a leakage resistance has been developed (see Japanese Laid-Open Patent Publication KOKAI No. 2003-169401).